1. Field of the Invention
The present invention relates to a sheet post-processing apparatus with an improved bundle claw of a sheet conveyor belt that conveys a sheet from a processing tray to a stacking tray and a sheet post-processing method.
2. Description of the Related Art
In a sheet post-processing apparatus, sheets stacked on a processing tray are conveyed to a stacking tray by using a sheet conveyor belt. The sheet conveyor belt is attached with a bundle claw. The bundle claw has a concave surface for regulating a position of a trailing end of stacked sheets to be conveyed and conveys the stacked sheets in an aligned state. Usually, the bundle claw has height sufficient for discharging a stapled sheet bundle of 100 or more sheets but a bottom surface of a concave portion for regulating a trailing end of the sheets is flat. With such a flat concave surface of the bundle claw, when a small number of sheets are conveyed, since a large space is formed in an upper part of the concave surface, a position of the trailing end of the sheets cannot be fixed on a lower surface side of the concave surface. Therefore, the trailing end slides to an upper surface side.
On the other hand, a motion of the sheet conveyor belt changes from a liner motion to a rotational motion in a position where the sheet conveyor belt comes close to the stacking tray. Therefore, when the sheets are conveyed in a state in which the trailing end of the sheets slides to the upper surface side, a bundle claw attached to the sheet conveyor belt rotationally moves at a point when the bundle claw comes close to the stacking tray, i.e., when the trailing end of the sheets is discharged from the bundle claw. At this point, the trailing end of the sheets is not located on the lower surface side of the concave surface of the bundle claw, where the trailing end of the sheets should be originally located, but is located on the upper surface side of the concave surface of the bundle claw (away from the rotation center of the sheet conveyor belt). As a result, speed of discharging the sheets falls increasing. Therefore, fluctuation occurs in paper discharge speed and the sheets are stacked on the stacking tray in a nonaligned state.
Japanese Patent Disclosure (Kokai) No. 2003-2636; H. Tamura et al.; Jan. 29, 2003 discloses a technique for controlling movement of a discharge belt 75 attached with a discharge claw 76 to thereby hold flat and align a trailing end of a sheet S and, as a result, eliminating a binding failure due to deformation of the trailing end of the sheet S.